This invention relates to oscillating force and pressure transducer systems of the type generally described in my U.S. Pat. Nos. 4,175,243 4,439,705 and 4,485,232 also upon the principles enunciated in my U.S. Pat. Nos. 3,891,870 4,020,448 4,067,241 and 4,126,801.
Transducers working on the foregoing principles have given excellent performance over certain force or pressure ranges but these ranges have been limited to a few tens of pounds or pounds per square inch because of the inability of the crystals to directly bear large forces.
According to the present invention oscillating quartz transducers capable of measuring much larger forces and pressures, which may be in the order of hundreds or thousands of pounds per square inch, is described. The new transducer contains a crystal which is similar in construction to that shown in my U.S. Pat. No. 4,485,232, FIG. 4. of which is reproduced again for reference in the present disclosure. This is a single plate-like oscillating crystal which sustains the force to be measured at its periphery by transmission of said force along the direction of the crystal surface in order to produce, in response to said force, a change of the resonant frequency of the crystal.
The force may originate from a fluid pressure to be measured, this pressure being applied to a diaphragm which forms part of the transducer enclosure.
The plate-like crystal of my U.S. Pat. No. 4,485,323 has on it two oscillating portions. As described in that Patent, the force to be measured was applied along the direction of the crystal surface and across one of the two oscillating portions by two seatings located on opposite sides of said oscillating portion. The edge of the crystal was arranged to be indented into the surface of each seating by a substantial overload force, as described in my U.S. Pat. No. 4,126,801, thus providing a short, but well-defined, length of support of the crystal edge on the seating. This permitted accurate measurement of the force, in the normal range of force measurement of the instrument, by bringing about a precise frequency change of the oscillating portion of the crystal across which the force was applied. Such a construction method, although excellent for smaller forces to be measured by the transducer, resulted in significant limitation in the amplitude of said forces because of the close proximity of the amplitude of the strain in the quartz to the strain failure amplitude of the quartz in the compressional mode.